(1) Field of the Invention
The present invention relates to a developing unit for developing an electrostatic latent image formed on a recording medium and, more particularly, to a developing unit comprising a developing tank containing a developer and a toner hopper (toner supply portion) for supplying toner to the developing tank as required such that the developing tank and the toner hopper can be separated from each other, in which the developing tank is detachable.
(2) Description of the Prior Art
An image forming apparatus, e.g., a copying machine and a laser printer, utilizing electrophotography, has a developing unit which attaches toner comprising a coloring pigment to an electrostatic latent image formed on a photosensitive body serving as a recording medium, e.g., electrostatically, in order to visualize the electrostatic latent image.
The developing unit has a developing roller for conveying the developer to a developing area opposing the photosensitive body. The developer stored in the developing tank is attracted to the developing roller by a magnetic force, and is conveyed to the developing area of the photosensitive body. Usually, the developing unit uses a developing roller obtained by forming a non-magnetic cylindrical sleeve around a magnet so that the developing roller magnetically attracts the developer by the magnetic force. When the sleeve is rotated, the developer is magnetically attracted to the sleeve by the magnetic force of the magnet, and is conveyed to the developing area opposing the photosensitive body. A magnetic brush of the developer is formed at a portion of the photosensitive body corresponding to the magnetic pole of the magnet. The magnetic brush rubs against the photosensitive body, thereby developing an electrostatic latent image.
The magnetic brush type developing unit having the above arrangement uses, as the developer, a two-component developer consisting of carrier as a magnetic body and toner as a coloring agent, a mono component developer in which the toner itself contains a magnetic material, and the like.
Some developing units perform development by utilizing non-magnetic mono component toner without employing the magnetic brush phenomenon. In this developing unit, since the developing roller does not have a magnetic force, it cannot magnetically attract the toner. Instead, non-magnetic mono component toner is coated on the surface of the developing roller by using a coating member, and the toner is conveyed to a developing area opposing the photosensitive body by rotation of the developing roller. Since this toner does not contain a magnetic material, it is very advantageous when forming a color image.
The developing unit has a developing tank storing a developer and a toner hopper for supplying toner to the developing tank. The toner is supplied to the developing tank as required. More specifically, when the toner in the developing tank becomes short, the toner in the toner hopper is supplied to the developing tank. This is because the toner which is consumed by development must be supplied to the developing tank as required. The toner hopper stores a large amount of toner and supplies it to the developing tank. In order to replenish the toner from the toner hopper to the developing tank, the toner supply port of the toner hopper opposes the toner replenishing port formed in the upper portion of the developing tank.
Conventionally, a toner hopper and a developing tank are integrally provided. When the toner in the toner hopper and developing tank runs out, the entire developing unit is replaced with a new one. Since the developing unit is replaced only because the toner runs out regardless of the service life of the developing unit, it is economically very wasteful. Therefore, it has been proposed to make the toner hopper and the developing tank separate from each other, and to make only the developing tank detachable, so that the developing tank is replaced when its service life runs out. Alternatively, it has been proposed to simplify the maintenance procedure of the developing tank.
When the developing tank is to be separated from the toner hopper so that only the developing tank is mounted or detached, it is necessary to prevent the toner from scattering or dropping from the toner supply port of the toner hopper and the toner replenishing port of the developing tank. For this purpose, a shutter or the like is provided, so that the toner replenishing and supply ports are closed when mounting and detaching the developing tank.
For example, Japanese Patent Application Laid-open Hei 3 No. 75769 proposes a developing unit as shown in FIG. 11. A developing unit 100 of FIG. 11 is constituted by a developing tank 101 and a toner hopper 102. The developing tank 101 has a developing roller for conveying a predetermined amount of developer to a photosensitive body on which an electrostatic latent image is formed, thereby visualizing the electrostatic latent image. The toner hopper 102 is detachably provided to the developing tank 101 and replenishes toner. An opening/closing member 104 attached with a shutter 103 is rotatably axially supported by a support shaft 105 in the developing tank 101. When the opening/closing member 104 is operated, the shutter 103 closes or opens a toner replenishing port 101a of the developing tank 101 by the biasing force of a spring 106.
An opening lever 107 for opening the shutter 103 is fixed to the toner hopper 102. The distal end of the opening lever 107 opposes a projecting portion 108 integrally formed on the opening/closing member 104. In order to close the shutter 103, a closing lever 110 rotatably supported by a shaft portion 109 is further provided as part of the developing tank 101 such that it opposes the projecting portion 108. A pivot force in the counterclockwise direction normally acts on the closing lever 110 because of the biasing force of a spring (not shown).
Therefore, in the state shown in FIG. 11, in the process of mounting the toner hopper 102 from above, the opening lever 107 abuts against the projecting portion 108 to revolve the opening/closing member 104. The shutter 103 opens the toner replenishing port 101a, and the opening lever 107 stops upon abutting against the closing lever 110. When the toner hopper 102 is lifted upward, the closing lever 110 disconnected from the distal end of the opening lever 107 is revolved counterclockwise, and is engaged with a pin 111 fixed to the opening/closing member 104, thereby revolving the opening/closing member 104 counterclockwise against the biasing force of the spring 106. As a result, when the spring 106 moves over the support shaft 105 by the pivot movement of the opening/closing member 104, the spring 106 revolves the opening/closing member 104 in the closing direction. Thus, the shutter 103 closes the toner replenishing port 101a. This closing state is maintained by the biasing force of the spring 106. At this time, the pivot movement of the closing lever 110 is regulated by a stopper (not shown), so that it will not interfere with the shutter 103 that closes the toner replenishing port 101a.
Inversely, when mounting the toner hopper 102 to the developing tank 101, the opening lever 107 is revolved downward upon abutting against the projecting portion 108 of the opening/closing member 104, and then the shutter 103 revolves to open the toner replenishing port 101a. When the spring 106 is located below the support shaft 105 in FIG. 11, the spring 106 serves as an opening biasing force for rotating the opening/closing member 104 clockwise. Thus, as shown in FIG. 11, when a supply port 102a of the toner hopper 102 and the toner replenishing port 101a coincide, the closing lever 110 abuts against the opening lever 107, so that the projecting portion 108 is separated from the opening lever 107. Note that reference numeral 112 denotes a supply roller provided along the toner supply port 102a. The toner is supplied upon rotation of the supply roller 112.
In the developing unit having the above arrangement, when the toner hopper 102 is removed upward, the developing tank 101 can be removed from the main body of the copying apparatus.
In the conventional developing unit 100 shown in FIG. 11, since the toner replenishing port 101a of the developing tank 101 is closed with the shutter 103, the toner will not drop when extracting the developing tank 101. However, before extracting the developing tank 101, the toner hopper 102 must be lifted upward. Then, the toner attaching to a portion near the toner supply port 102a sometimes leaks to drop or scatter.
Furthermore, to extract the developing tank without touching a photosensitive body, the developing tank must be moved in a direction perpendicular to the direction of the rotating shaft of the photosensitive body and be separated from the photosensitive body so that the surface of the photosensitive body will not be damaged. For this reason, while separating the developing tank from the photosensitive body, the toner supply port of the toner hopper and the toner replenishing port of the developing tank sometimes rub against each other, thus scattering or dropping the toner. When separating the developing tank from the photosensitive body and extracting the developing tank, the toner replenishing port and the toner supply port only shift laterally relative to each other and are not disconnected from each other. Then, the toner scatters or drops often due to vibration occurring when the toner replenishing port and the toner supply port rub against each other. In this case, even if the toner replenishing port and the toner supply port are slightly separated from each other, they may come into contact with each other due to vibration occurring during extraction of the developing tank, and the toner sometimes scatters from the toner supply port.
In Japanese Patent Publication Hei 5 No. 13315, a developing tank is pivotally provided so that it can be separated from a photosensitive body. The developing tank is mounted or detached while it is separated from the photosensitive body. In this case, while mounting the developing tank, a shutter closing the toner replenishing port of the developing tank is opened in an interlocking manner with the mounting operation, and the toner supply port of a toner hopper and the toner replenishing port of the developing tank are coupled to each other with a bellows-type coupling member fixed to the developing tank. This coupling member is housed in the shutter mechanism of the developing tank. When the shutter is opened upon mounting the developing tank, as the coupling member is constantly biased in a direction to couple the toner replenishing port and the toner supply port, they are coupled. When this coupling operation is completed, the developing tank is revolved toward the photosensitive body and is thus positioned in the developing state.
With this arrangement, since the toner supply port of the toner hopper and the toner replenishing port of the developing tank are coupled with each other in an interlocking manner with the mounting operation of the developing tank, when mounting the developing tank, the shutter provided as part of the toner hopper is opened, without any problem, in an interlocking manner with the mounting operation. Thus, toner leakage and the like can be prevented.
When, however, extracting the developing tank, the developing tank-extracting operation must be started only after the developing tank is separated from the photosensitive body. Otherwise, the shutter of the toner hopper is not closed, so that the toner cannot be prevented from dropping or scattering due to vibration occurring during the extraction. Furthermore, since the member that couples the toner supply port and the toner replenishing port is constantly biased to seal them, no means is available for separating the toner replenishing port and the toner supply port. This makes the extracting operation very difficult. In particular, since the coupling member is housed in the shutter of the developing tank, the toner attached to a portion near the shutter soils an operator's hand, and also a very cumbersome extracting operation is required. If the operator forgets to house the coupling member, extraction of the developing tank is interfered and thus the tank cannot be extracted.
As described above, although the developing tank can be mounted and detached after it is separated from the photosensitive body, the mounting/detaching operation of the developing tank, particularly the detaching operation, is very cumbersome. Since the coupling member is coupled to the toner supply port of the toner hopper in an interlocked manner with the mounting/detaching operation, or is separated from the toner supply port of the toner hopper manually, toner contamination caused by the toner that scatters or drops due to vibration occurring during the coupling or separating operation cannot be prevented.